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How Hot Would a Light Saber Really Be?

Datagod asks: "Has anyone ever calculated the temperature you would need to be able to slice through steel like it was thin air? How hot would a light saber really need to be? Also, I am assuming that at least some of the metal would be vaporized and the expanding gas would fling bits of molten metal at the saber wielder. Wouldn't your average Jedi be horribly scarred from all this."

7 of 410 comments (clear)

  1. Re:Very hot. by kryten_nl · · Score: 5, Informative

    Very, very cold.

    As the anti-protons move at uniform speed and the temperature is defined by the relative speed of particles wrt the flow.

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  2. All your answers ... by psergiu · · Score: 5, Informative

    ... are HERE .

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  3. It's not an issue of just temperature by xiphoris · · Score: 3, Informative

    It's an issue of temperature AND power.

    Consider this: how hot does something have to be to melt an ice sculpture? Well, a match would do it, except a match can't provide the power necessary to melt a significant amount of ice.

    You need the temperature necessary to turn steel into a vapor (look that up on a periodic table of elements); you also need the power necessary to turn some mass (per second) of steel into vapor. Anyone with a background in chemistry should be able to look up the required information on a standard periodic table.

    The equation will look like this:

    (Steel's specific heat) * (volume of steel to vaporize per second) * (temperature difference) = power necessary.

    1. Re:It's not an issue of just temperature by Troed · · Score: 3, Informative

      Steel the common name for the pure form of Iron

      Uh no. Steel is the name given to various Iron alloys. Iron is the name for the pure form of ... Iron. You got it exactly backwards.

      Yes, I'm a Mechanical Engineer.

  4. Re:Wickedlasers by kaan · · Score: 4, Informative

    omg for a second there i thought you posted a url to http://wickedweasel.com.

    *phew* that was close!

  5. Re:Shadows by Ruie · · Score: 4, Informative
    I remember getting scolded by some fanboys for suggesting that lightsabers should cast no shadows (apparently they must cast shadows since shadows were present in Episode 4...) because the cutting edge - whether plasma or whatever else - would need to be hairline-thin regardless of temperature in order to slice through things without causing unmanageable explosions of melted and vaporized target material.

    Well, assume for a moment that it works. To melt metal one needs a lot of energy - so it likely comes from a nuclear source.

    1kg of steel has specific heat of 448 joules per degree Kelvin.

    Energy from fusion of hydrogen atoms is at most 8 Mev, the energy stored in Hafnium atom is 3 Mev - let's assume that the agent used has weight of Hafnium but produces 1 Mev per atom.

    Thus 1kg of energy agent stores 9e10 Joules - plenty enough to heat 20e3 tonnes of steel to 10000 degrees - cool !

    So, as long as I am having fun, here is a "complete" light saber design - just so that no one tries to patent something that obvious:

    • Handle - let's separate in two compartments - one contains energy agent and the other initiator that bombards that agent with nuclear particles.
    • In response to bombardment energy agent produces new particles in much greater proportion - this is a sticky point as single pass stimulated emission amplification is likely not that efficient - but then we have power to spare ! In fact this might be a feature as the handle will last very long time - the amplification medium will deplete slowly and from one end.
    • the particles are passed through moderator which limits their mean path in air to desired length.
    • put peltier element around the energy agent and moderator and feed the energy into the initiator.
    • initiator could be made as short pulse laser striking metal foil - these have been tested as tabletop devices already and should be capable to produce 3Mev gamma rays.
    • move the initiator around as energy agent is used up.
    The particle fountain would be very narrow - but it will heat up the air and that would produce the glow. Oh - and plasmas are opaque to light so there will be a shadow.

  6. Re:2nd post by cekerr · · Score: 5, Informative

    When I clicked on the link:
    "The House Subcommittee on Modern Intergalactic Weapons Development and Regulation"
    My Firefox browser was hijacked, endless screens opened up and somebody's voice came over the speaker saying I know not what. One of the screens was an unpleasant image.
    OK, I've been April Fooled. But I doubt it was the sort of thing slash.dot approves of and if it does, I'm disapointed.
    Yes, I know all sorts of clever people can hijack my computer via malicious links. But I had hoped for better standards around here.
    I'm now on the 4 hour virus scan/spyware checking cycle on my laptop. Just as well it's Saturday.